(1) The HIV protein Rev is an essential for viral replication controlling expression of regulatory and structural proteins. The structure of Rev has not been determined due to the physical and conformational heterogeneity of protein produced by recombinant DNA. We have made extensive modifications of the Rev protein in order to improve its solubility for structural work. In addition, we are attempting to further stabilize Rev by forming binary complexes with either antibodies or tubulin. To generate a wider range of monoclonal antibodies for co-crystallization studies, we have made recombinant antibodies based on phage display selection. Bone marrow from immune rabbits was used to create an antibody library. Rev binding monoclonal antibodies (mAbs) were selected then humanized producing chimeric mAb fragment antigen binding portions (Fab). These Fabs contain rabbit variable domains and human constant domains and were produced in bacteria using an E.coli secretion system. One such produced Fab bound to HIV-Rev with high affinity and depolymerized the normally highly associated Rev protein forming a physically homogenous low molecular weight immune complex. The Fab-Rev complex was crystallized and the Rev structure determined by X-ray diffraction methods. Refinement of the structural model is currently being performed and the details when published may help in the design of novel anti-HIV drugs. Furthermore, the high affinity humanized anti-Rev Fab alone may also have potential therapeutic use and this also is being investigated. (2) HIV protease, a homodimeric protein is essential in the viral life cycle and a major anti-HIV drug target. Peptides derived from the N- and C-terminal regions of the HIV-1 protease dimer interface inhibit protease activity by preventing dimerization (monomeric protein is inactive). In previous work, it was shown that the solubility and cell permeability of the peptides was enhanced by linking the transduction domain of HIV-Tat. Methods for studying the mechanism of the dimerization inhibition were developed using HIV-proteases with mutations to facilitate biochemical and biophysical analysis. For example, a multidrug resistance HIV-protease, identified from clinical samples and which does not undergo self digestion (autolysis), was produced in bacteria using recombinant DNA methods. This protease, resistant to drugs binding to the active site can be inhibited by peptides binding to the dimer interface, was studied using a simple and novel approach. These studies may contribute towards the development of new anti-HIV drugs.